232 Dr. F. E. Fritsch. On the Subaerial and [Jan. 2, 



var. angusta, Hass. in Tissawewa), whilst I never met with a Zygnerna in any of 

 the tanks. Looking at the species of Spirogyra found in the Ceylon fresh- 

 waters in their entirety, it is very noticeable that they all belong to the 

 section in which the transverse walls between the cells are simple and not 

 infolded, and that the large majority have more than one or even two spiral 

 chromatophores in each cell. These features are, in the main, common to all 

 the Spirogyras of tropical waters, although they do not appear to have been 

 noted before. Of 38 species recorded from the tropics, only nine* have cells- 

 containing a single chloroplast, and only five have infolded transverse walls. 

 Infolding of the end- walls of the cells is commonly met with in many of the 

 narrower Spirogyras of our waters, and is generally regarded! as a mechanism 

 for the dissociation of the cells of the filament, but its exact function is not 

 perfectly understood, nor do we know why it occurs in one species and not 

 in another. Since the large majority of tropical Spirogyras are broad forms,, 

 and infolded walls are only found in the narrower species, we could in no case 

 expect to find many examples of the latter type; yet the interesting facfc 

 remains that the few narrow forms nearly all have simple end- walls. It is just 

 as difficult to account for the prevalence of broad forms with numerous closely- 

 arranged chloroplasts in each cell. Except for the species of Pithophora, the 

 Spirogyras are the only Algse with broad filaments found at all commonly in 

 the tropics, all the remaining forms being narrow and rarely exceeding 15 ^ in 

 diameter. I am inclined to associate this with the fact that Spirogyra gets on 

 well in stagnant water under relatively unfavourable conditions of respiration 

 (perhaps owing to the thin cell-wall), so that forms with broad filaments are 

 as successful as the narrow ones {cf. next paragraph and also p. 221). I am 

 unable to offer any explanation for the usual abundance of chloroplasts. 



The most important forms in the attached green algal flora are species 

 of (Edogonium.% Floating masses of this genus are rather rare (only in 

 Madokotaikulam and Madakanawewa), although this may be a seasonal 

 phenomenon. The species of (Eologonium found in the waters of Ceylon 

 are, as a rule, narrow forms with filaments having a diameter of 9 — 12 //,, 

 even 15 /jl being rather rare ; species with broad filaments are exceptionally 



* Sixty-two records of Spirogyras, with a number of chloroplasts, as compared with 

 20 records of forms with a single chloroplast. The details will be given elsewhere 

 (Fritsch, in ' Annals of Botany,' vol. 21, No. LXXXII, April, 1907, p. 260 et seq.). 



t Cf. Oltmanns, loc. cit., vol. 1, 1904, pp. 57, 58. On the whole, my material shows very 

 few cases of breaking up of the filaments into their constituent cells, though the 

 conditions must frequently have been favourable for dissociation. This is probably due 

 to the absence of those species of Spirogyra (viz., those with infolded end-walls), which 

 most commonly exhibit this phenomena. 



I The genus Bulbochcete is of rare occurrence in the tanks, and was always only 

 observed in small quantity amongst other attached Algse. 



